Gram staining is one of the most frequently performed procedures in modern microbiology laboratories. Such procedures are used to broadly classify bacteria as “Gram-positive” or “Gram-negative.” After affixing a bacteria-containing sample to a microscope slide, the sample is treated using staining reagents such as crystal violet in combination with Gram's iodine. This first step stains all bacteria a deep blue or violet. The principal difference between “Gram-positive” and “Gram-negative” bacteria is that in “Gram-positive” samples, the staining reagents are absorbed within the whole cellular structure, while in the “Gram-negative” samples, staining occurs only superficially. Consequently, when the sample is subsequently treated with a decolorizing agent (such as acid alcohol), Gram-negative bacteria tend to lose their color, while Gram-positive bacteria remain stained blue or violet.
Gram stains are conventionally prepared and analyzed manually. Manual Gram staining is labor-intensive, requires skilled personnel, and may fail to achieve optimum staining characteristics in the sample set. Non-optimum staining may result in false Gram-positives as well as false Gram-negatives.
There have been different attempts to automate the Gram staining procedure. See, for example, U.S. Pat. No. 4,029,470 to Wilkins et al. (“Wilkins”). Similarly, the Aerospray Slide Stainer, available commercially from Wescor, Inc. of Logan, Utah is a rudimentary automated staining apparatus. Other staining devices include the Midas III Slide Stainer, commercially available from Merck KGaA of Darmstadt, Germany; the Poly Stainer, which is commercially available from IUL Instruments GmbH of Koenigswinter, Germany; and the Automated Gram Stainer, commercially available from the GG&B Company of Wichita Falls, Tex. and described generally in U.S. Pat. No. 6,468,764 to Gibbs et al. None of these instruments or techniques, however, allow for the capability of applying staining and/or decolorizing agents before, during, and/or after examination and/or image processing of a sample slide.
Consequently, there exists a need for an improved automated staining method and system.